1. Field of the Invention
This invention relates to a fluorescent display apparatus for displaying numerals, characters, graphic forms or the like in a high density matrix form without having any display imperfection.
2. Description of the Prior Art
A fluorescent display apparatus forms a display by impinging electrons emitted from energized filamentary cathodes unto anodes on which is deposited phosphor layers, and to which an anode voltage is selectively applied. The fluorescent display apparatus can be driven at a low voltage for effecting a luminous display of sufficient brightness and is low in power consumption which enables it to be directly driven by a LSI. Furthermore, various luminous colors are obtainable depending upon the phosphor to be used. Because of these advantages inherent in the fluorescent display apparatus, it is widely used as a display device for various electric appliances and the like.
Recently, there has been a demand for a fluorescent display apparatus which is capable of displaying not only numerals or characters but also any optical graphic forms or pictures to be reproduced in a high resolution so as to achieve distinct and intricate displays.
In order to meet such a demand, a dot-matrix type fluorescent display device as shown in FIG. 1 has been proposed and put into practical use in which a plurality of rectangular or circular micro-electrodes arranged on a plane are driven in a matrix fashion. More particularly, the dot-matrix type display device, as shown in FIG. 1, includes a plurality of stripe-like anodes 1 disposed on a substrate (not shown) and phosphor layers 2 coated in the form of rectangle or circle on the anodes 1 so that each of the phosphor layers 2 forms a single display element. Above the phosphor layers 2, a plurality of mesh-like control electrodes 3 are arranged opposite to the phosphor layers 2 so as to extend in the direction perpendicular to the anodes 1. Electrons emitted from a cathode (not shown) impinge on the phosphor layers 2 located at the position where the anodes and the control electrodes respectively having an anode voltage and a control voltage selectively applied thereto cross each other, resulting in the phosphor layers emitting light. A display in the form of letters, figures or the like is accomplished by combining the light emitting phosphor layers as desired.
As stated hereinabove, the conventional dot-matrix type fluorescent display device is generally constructed in the manner that the matrix is composed of the anodes 1 and the control electrodes 3, and the phosphor layers 2 located at the position where the selected anodes and control electrodes cross each other and they are energized by electrons to effect light emission.
In order to improve the density of a display in the dot-matrix type display device, it is required to arrange the phosphor layers 2 with a narrow interval defined therebetween. This results in the control electrodes 3 having to be disposed at narrow intervals. However, such arrangement of the control electrodes results in electrical fields generated from the adjacent control electrodes affecting the path through which electrons impinge on the phosphor layers to cause display defects to occur, thereby deteriorating the quality and clearness of a fluorescent display.
Such display defects are explained with reference to FIG. 2. In FIG. 2, reference numerals 2a and 3a designate a phosphor layer to emit light of phosphor layers 2 and a control electrode disposed opposite to the phosphor layer 2a, respectively. On both sides of the electrode 3a, control electrodes 3b are disposed adjacent thereto. When an anode voltage and a control voltage are respectively applied to an anode 1 and the control electrode 3a, electrons e emitted from a cathode impinge on the phosphor layer 2a to allow it to effect light emission. However, the control electrodes 3b adjacent to the electrode 3a are applied thereto a negative voltage identical with or below the voltage of the cathode to generate negative fields. This results in the path of electrons being curved, so that electrons may not impinge on the periphery of the phosphor layer 2a thereby generating display defects.
The less the interval between the control electrode is, the greater the display defects. Such display defects become a serious problem in the case of producing a display of a high density in the dot-matrix type fluorescent display device.